I had to use close to max VG for a long time (PG sensitive) and yes, it needs a longer steep. Although, once I started using PEG400 instead, I found I really didn't need more/less flavor (and I typically steep 6 weeks sometimes longer) but that the flavor was sharper, crisper, etc. As I researched it, I did find that PEG400 is a flavor carrier, like PG.
I don't think UPPING my flavoring would have been a solution, honestly because it wasn't LACK of flavor exactly it was kind of this muting/muddy sort of taste to the flavors. Although I guess you could TRY a higher percentage and see what happens. I mean, do a set of testers at various percentages and get yourself in a ball pack or flavoring because honestly, at the time I wasn't complaining, so I didn't up anything but I remain unsure how much it would have remove the "muddy" effect (and also keep in mind, the more flavor percentage with MOST flavors, the more PG you will be adding, so that may have an effect.
Best of luck,
Anna