Going to Ground is a “product” of doctrine and training. I have personally eaten my fair share of dirt. Volume of fire has nothing to do with it. A single sniper shot will do just fine most of the time. Just not healthy to stand up and look around to see where that shot came from.
Suppression is something else again. This, IMO, is a volume of fire at a particular point which either keeps the target from returning fire, forces the target to move to another location (which experienced or well trained troops will be doing anyway — fire and displace – I think they did that in WWII didn’t they?), or if the target does return fire, that fire is hurried and hopefully less accurate.
They can be similar in some respects but are not identical.