Paul, say you have six 200watt 42volt 5amp panels. There are three main ways in which they could be connected, all resulting in a 1200 Watt array.
(A) All panels connected in Series, giving 5 Amps at 250 volts.
This is the least efficient option in good light, and gives a "low light" charge rate of about 1 Amp.
(B) Three paralleled pairs, each of 2 panels connected in Series, giving 15 Amps at 84 volts (so your setup must be somewhat similar).
This would give a "low light" charge rate of about 3 Amps.
(C) All panels connected in parallel, giving 30 Amps at 42 volts.
This is the most efficient option in good light, and gives a 6 Amp charge in "low light" conditions.
You can see that the higher the voltage, the lower the current and the poorer the performance, especially in low light conditions.
It might be worth reconfiguring your system. A "re-jig" could double its performance in low light - when it really matters. As is, your 1200 watt system stands to give you a substantial power surplus in Summer, but fall short on very cloudy days, especially in Winter and/or Southern latitudes.