You are right 5miles. The point is the aircraft starts out "really" IFR, and stays so until he reports "VFR on top" and we clear him to "maintain VFR on top". The fact the pilot doesn't tell me what level he is climbing to means I HAVE to restrict him if something is in the way. Once my aircraft assigned FL150 has broken through and been so cleared he can cruise at any VFR level he likes appropriate for his direction of flight.
Once he is VFR on top (sh*t, I hate that phrase), yes Galah, if he was heading west he might want to stay at FL145, but he can climb to FL165 if he wants to.
The goobers are very stern (in the book anyhow) about standard levels. VFR stay at the appropriate VFR level or don't fly. Above 3000 agl IFR stay at the appropriate IFR level, unless if they ask really nice they may get the opposite IFR level. I don't know why, but we don't have the same proscription. If you heart yearns to fly at FL165 we can approve it. Probably a hole left over from Dick's previous half-baked efforts to sell us E airspace.