The difference is the Irbis-E has two TWT transmitters, while the Bars has a single one.
Well the gain from just a single Chelnok 10 KW TWT from Irbis wont make much tbh. Like Irbis was rated at 20 KW, peak means for duty cycle of 25%, you multiply that you got average power of 5 KW, that's for the claimed 350-400 km range.
While Bars have various rating from 4-7 KW with average power of some 1-1.75 KW. If we assume the Bars-R was provided with a single Chelnok with 10 KW.. then you'll have 2.5 KW average power. You can easily find the range gain by 4th root factor. (2.5/1.75)^(1/4) = 1.093 or gain of some 9%. Not sure how it will help R-37.
Unless somehow Russians just accept that they wont be maxing out the R-37 for Su-30 family.