i've heard that said several times - from watching some highlights, they seem to be okay at running people off the 3-pt line at time (although opponents have gotten hot - they've given up 8+ 3s 14 times), but they then meet them in the lane, with poor close outs in the mid range.
That said - the data doesn't especially back that up. Haslametrics (a site I love) tracks mid-range percentage and near-range percentage. For Miami-
They are very average allowing 32% on 3-pt shots (147th) and are below average allowing 39% of shots from deep
They are above average allowing 35% on mid-range shots (81st) and above average in limiting mid-range shots
They are very poor in allowing near-range shots (63%) and average in allowing over 28% of shots from near range. This is where their defense really struggles.
So given that, I'd love to see Hunter and IB being aggressive getting to the rim.
The goal of Haslametrics is to provide unique statistical insight and to offer predictive analysis based on teams' prior performances in a given season.
www.haslametrics.com