Different weapons have different range profiles. Also, infantry doesn't have same vision as range.
Mainline infantry can spot for themselves, we already know this is not the case for everything else. Profiles may be different but distance remains constant.
and yeah to be more specific, cons in heavy cover is suchhh a tough approach. you're gonna lose a few squad members if you decide to assault them, and sticking back, unless you're in equal cover isn't going to net you good results, nor is it exactly the most time efficient approach. if you do decide to assault a soviet position early you gotta do it with either, a 2:1 advantage, a supported flamer, or with a halftrack to mitigate the squad losses. the trick is not to let them entrench in the first place. much easier said than done.