As Forbisher just said - I have been running by "30 Amp" Epever BN with a nominal "500 Watt" Array for multiple years without any problems at all. When the batteries don't want to accept all the available Solar watts, the SCC needs to leave the "excess" power in the panels - either by intentionally adjusting the tuned Array Voltage away from the MPPT, or by falling into "PWM" on the Solar side (rapidly disconnecting and reconning the array, leaving power unused within the panels).
My old "big iron" MPPT definitely used both PWM and MPPT mode on the Solar side. I'm not sure whether the EpEver "BN" also has both mechanisms, or runs with only the MPPT "mis-tuning" tactic. The maximum power delivery of a "40A" Tracer BN varies according to Battery Voltage - at the 14.5V value which I use to charge my LFP batteries, it could push 580 Watts into the Batteries and simultaneous "12V" DC loads. The maximum panel power which it could utilize is 580 Watts divided by ~ 95 percent efficiency, depending on the MPPT versus battery voltage differential. So it can actually utilize about 610 watts of PV power delivered at the Tracer terminals. From the panels above, you're also losing some power in the Solar Wires - so you might be using perhaps 630 watts. as generated right at the panels. Lead-Acid batteries are charged at somewhat lower voltages.
"800 Watts" of nominal panels will only deliver about 800 watts for a few minutes, near Solar Noon, on a perfect and cloudless day WITH panels pointed straight at the noon-day sun. If your "30A" SCC would like to use all 610 watts for a full hour, or even 2 hours, then 800 watts of panels sounds like a pretty good match too me - your maximum power Solar Day (at 630 watts actually delivered) extends well before "noon" and well "after "noon as well. Delivered power rises to 630 watts in the late morning, and remains constant until early afternoon, falling off later. If your panels are not at the best angle (mine for example, are flat on a horizontal roof), then you need even more nominal "Panel Power" to utilize the controller completely, for an extended period of time.
The EPEVER "BN" manual lists maximum usable power, with no mention of maximum configurable power at all. I SWAG the maximum configured power to be almost nearly twice as large, for an installation like mine (horizontal panels fixed panels with no tracking on either axis). On my 30A, I'd probably be good with 800 nominal watts on my flat RV roof. (Although I don't need "maximum panels" right now, because my small battery bank always gets charged mid-afternoon anyways, with a couple of good hours left unused). With a 40A, I'd be comfortable going all the way to 1100 watts, maybe even 1200.