Firstly, MPPT charge starts only if the PV with a voltage difference higher than the battery. Usually this voltage difference should be higher than 3V at least.
Secondly, all MPPT device may have a limit on max input voltage. For example, Helios’s MPPT controller VENUS-M2440 with a max input of 100Voc, so this 100Voc (PV open circuit voltage, not rated voltage or working voltage) is the limit, and you can not plug in arrays over this limit. * usually 100Voc means 75V around of working voltage.
Thirdly, if the voltage difference between the battery and PV is too much, then we may have a not small power loss, so we need to control the array voltage by connection more parallel and less series on panels. For example, for controller VENUS-M2440 (12/24V), if you have 2 panels of 36V, then it’s better to make them connect in parallel (36V), but not in series (72V). However, it’s not really a big deal, the difference could be very small. If you find it’s not convenient to make the modules connected in parallel, then just do it by series.