if that 13.5v is the tri's readout, confirm it with your handheld meter.
the boondocker's are not set exactly to 14.6v and 13.6v, but fairly close. mine goes into float (~13.2v) only after about 8.5 hours of continuous charge. yours may do different?
and my particular 6v's are full at a resting voltage of at least 12.78v, so yours may be higher, as well. the charts are a general guideline, and not to be taken literally.
and by resting, i mean sitting with absolutely no loads for that 1 to 3 or 4 days. which means a proper resting voltage can only truly be done while the bank is out of service. but once you know what it takes to fully charge your bank, you can rely on the amps-at-volts charge parameters... such as say 1.8a at 13.6v.