[Goose]

Wouldn't the Russians fleeing be in range of Ukraine's longer range self propelled artillery?  Krab's, M109, Zuzana, and Caesars all might stand a chance to hit river crossing Russians if they are moved to the recently liberated Ukrainian towns.  Would that be too risky though?

I suggest looking at https://twitter.com/TheStudyofWar/status...40/photo/1. This map shows that there are no "blue areas" closer than about 30km from the boundary of Kherson city. The bridges across the river are about another 10 km away. Unless they are sitting right on the front lines and firing RAP, the M109s can't reach the bridges. The Zuzana uses a 155mm/L45 (or L52 in the -2) that can just barely reach. The Krebs and Caesars also uses an L52 gun. Obviously, sitting on the line of contact isn't viable. It is also important when considering range to specify the ammunition type. RAP and Excalibur will go further, but Ukraine doesn't have enough of either to generate continuous fire missions over days of fighting. Just to be clear, all these guns use "NATO standard" 155 mm ammunition. These rounds go further when fired by longer guns, thus the L52 guns outrange the L42 and L39 firing the same ammunition.

The standoff distance for towed artillery is often given as 1/3 the range, meaning that an M777/L39 needs to be 1/3 * 22.5 km behind the lines, or about 7.5 km. This standoff is a rule of thumb, not absolute. Self-propelled artillery can be much closer to the FEBA, but the corresponding important constraint is that their supply vehicles generally don't want to be. It is also necessary that the self-propelled artillery have room to disperse and reposition in order to survive counter-battery. Therefore a narrow salient isn't ideal as a firing position. To interdict the retreat by fire, Ukraine needs the ability to deliver sustained artillery fire at the crossing points. They are still too far away to do that. They need to get closer by 10-15 km on a fairly broad front near Kherson city. It is much worse around Nova Kakhovka, unfortunately.

[Goose]

Wouldn't the Russians fleeing be in range of Ukraine's longer range self propelled artillery?  Krab's, M109, Zuzana, and Caesars all might stand a chance to hit river crossing Russians if they are moved to the recently liberated Ukrainian towns.  Would that be too risky though?

I suggest looking at https://twitter.com/TheStudyofWar/status...40/photo/1. This map shows that there are no "blue areas" closer than about 30km from the boundary of Kherson city. The bridges across the river are about another 10 km away. Unless they are sitting right on the front lines and firing RAP, the M109s can't reach the bridges. The Zuzana uses a 155mm/L45 (or L52 in the -2) that can just barely reach. The Krebs and Caesars also uses an L52 gun. Obviously, sitting on the line of contact isn't viable. It is also important when considering range to specify the ammunition type. RAP and Excalibur will go further, but Ukraine doesn't have enough of either to generate continuous fire missions over days of fighting. Just to be clear, all these guns use "NATO standard" 155 mm ammunition. These rounds go further when fired by longer guns, thus the L52 guns outrange the L42 and L39 firing the same ammunition.

The standoff distance for towed artillery is often given as 1/3 the range, meaning that an M777/L39 needs to be 1/3 * 22.5 km behind the lines, or about 7.5 km. This standoff is a rule of thumb, not absolute. Self-propelled artillery can be much closer to the FEBA, but the corresponding important constraint is that their supply vehicles generally don't want to be. It is also necessary that the self-propelled artillery have room to disperse and reposition in order to survive counter-battery. Therefore a narrow salient isn't ideal as a firing position. To interdict the retreat by fire, Ukraine needs the ability to deliver sustained artillery fire at the crossing points. They are still too far away to do that. They need to get closer by 10-15 km on a fairly broad front near Kherson city. It is much worse around Nova Kakhovka, unfortunately.