Are u talking about base crew or support weapons recrewed by conscripts?
If it's for the first, has there been any change to that?
If it's for the 2nd, this happens with all recrewed weapons. Not sure how to lower effectiveness on that specific scenario. I mean, if you recrew an MG with Pio/RE, they will probably own non full member squad who decides to close in. Same thing happens if you attack a base OH support weapon close range with RET.
While FMR is active they stomp whatever due to the added armor (live) and the added 50% accuracy makes those low accurate mosins actually do something.
Crewed with conscripts. with other factions you only get 3 guys firing and you lose DPS very quickly, becoming a non-factor- the only ingame situation where i've seen crewmen affecting a fight as non-soviet factions was with, of all things, fallschirm-crewed weapons- but that's a heck of a niche case and expensive/slow to reinforce anyway.
Currently conscript crewed weapons are pretty unreliable, since conscripts already have bad accuracy and there's a further 25% penalty on crewmen, if I recall. Penal crewed weapons are obviously pretty strong but those do cost a fair amount more to reinforce. In the EFA revamp, the greatly buffed accuracy of conscripts even at the cost of damage makes their performance very consistent and quite strong.
FMR obviously gives them a buff, but the ability making team weapons virtually unflankable seems very unintuitive. If the ability made the crewed weapon better at it's role during the duration while still retaining its vulnerability to flanking that would be ideal.