I have about 3 years experience with MDMA, rolls and 5-HTP and I've used the 5-HTP in several different ways. I've never found that it reduces the roll, it has the opposite effect for me.
First off, I never take it with rolls. I only take it with Molly. I've taken it with rolls many times and I often wind up overheating. Not just sweating, but feeling physically flushed and hot to the touch. My skin felt hot and I could feel steam or heat coming off my shoulders and head. I had a few times where I felt like it was bad for me and I was close to crossing a line I didn't want to cross.
I've never had any problem with 5-HTP and Molly. If I have time to plan, I take 5-HTP the day before, and then again the morning I plan to roll. Then I will take it again in the afternoon the day I plan to roll, often around 4pm. I usually take Molly after 10pm. If we take it earlier I will skip the afternoon 5-HTP.
Then at least 3 hours after taking the first Molly I will sometimes take a 5-HTP if it crosses my mind. Most times it won't cross my mind until later. LOL
I take one at come-down, and one the next morning before I eat breakfast. Lately, I have only been doing Molly since there are no clean pills lately. I don't seem to need 5-HTP for any depression reason the next day, but I've used it for that in the past for rolls that were dirty and it comes in handy for that.
My advice is to use 5-HTP with caution, watch your body temp and water consumption, and be safe. The dose of the 5-HTP that I've taken is 200mg. I would think someone who is not experienced with rolling shouldn't take it, because you need to really know your body and be able to tell is you are too hot, etc. Also know what you are taking and only take it when you know you have MDMA.