I still don’t agree, as a generality. You get all kinds of IMC at all kinds of levels
Of course but we are talking the most likely forms not what you get once in 1000h of flying, it’s not rocket science that a cloud is likely to reach higher altitudes when it’s a vertical bumpy towered cloud unlike layered smooth horizontal one, basic weather ABC
For sure IMC at 200ft is 100% smooth stratus while IMC at 60000ft is 100% washing machine thunderstorm, you can extrapolate the average in between
Someone with an IR will have more of that selection or sampling bias: they fly more often in clouds and usually on higher eurocontrol levels and sometimes above hot or high terrain, so likely they found IMC getting way more bumpy that what it used to be on PPL (illegally) or on IMCR rating (under UK airspace)
If one uses IR to cruise VMC on top, they will find flying getting more smooth 
I’ve had IMC at FL370 and it was lumpy for 2 hours. Just high altitude crap at 36995ft lol.
