No doubt getting crushed under the reverse sit sucks balls! The GGBJJ Youtube channel also has a video about preventing the reverse sit & covers 1 sweep:
https://www.youtube.com/watch?v=L_hmWnJi-zc.
I found the advise to frame the knee very helpful when preventing the reverse sit. I'm not sure what type of bottom 1/2 guard you like to play but maybe try something different than whatever you are playing that opens you up to this technique. The lockdown game is my goto 1/2 guard for sure, however I have found it to be more effective once I started switching things up by using other bottom 1/2 guards as needed. It keeps me less predictable & if I keep getting smashed, flattened out, or reverse sat w/ my lockdown game I switch to 93 guard to keep more space & this also makes it easier to frame that knee.