Naps question

For those of you lucky mamas whose babies sleep through the night or only wake once - what do their daytime naps look like? We're trying to regulate our sons nap routine to hopefully help with night sleep. He sleeps after about 1.5 - 2 hours of wake time which is great but the length of his naps is all over the place. Sometimes 20 mins and sometimes 1.5 hours. I think the irregularity of the length is throwing him off but not sure. 
Any suggestions? 
Thanks in advance!