Putting money in the pot should always be done with a specific goal in mind. If your goal is fold out the limpers, then your raise needs to be big enough to not price them in. A general rule of thumb is to raise whatever your standard open would be + 1bb per limper. So if you normally open at 3x, with 2 limpers in front of you, you'd want to open at least 5x.
When you have a solid hand that beats most all limping ranges, you don't want to go to the flop 5 handed, you want to try and iso the calling stations by betting enough to fold out the tighter players but keep the station in. OTOH if you have a weaker hand with high implied odds
like a small pair or suited connector, you want to both risk less and
keep more people in the pot, so you bet smaller (or flat) to keep them in and see a flop to get paid off on.
And as far as 3x goes, that's a standard opening size in early tourney stages but generally too high as blinds increase. You typically want to scale down your opens to something like 2.75x, then 2.5x, then 2.25x, then 2.1x, etc. until you're just minraising (or shoving) at the higher levels. Opening 3x and having to fold to a 3bet or shove when stacks are short is just spewy.