The frame is definitely part of the circuit! One of the biggest causes of electrical problems on all bikes is poor grounds. Bright clean bare metal is needed. You can spray after assembly with an electrical contact cleaner/sealer.
The engine must be grounded securely to the frame. The main engine-battery connection is via the battery ground wire, a heavy wire from negative terminal to the speedo cable fitting bolt at the right rear of the transmission.
The coils aren't grounded in the stock setup.
There are a couple of ground connections at various points on the wiring harness, be sure they are well-grounded. One of them has several wires coming to one connection under the tank, usually to one of the coil mounting screws - be very careful it's a good solid clean connection, it's very important.
Inside the alternator cover there is a ground connection for the diode board - there is also an additional harness available from your dealer that improves the connection - worth getting. I think it's part #12 31 1 468 013
While you're in there be sure your diode board has solid aluminum mounting, not rubber.
Check the main positive B+ wire - 4mm red - from the diode board to the starter - if it looks cooked or stiff and brittle replace it. Also check the main positive wire from the starter to the battery. All other alternator/diode board wires should be checked for signs of aging, brittleness etc and replaced if in any doubt.
I'd also scrape the engine and frame mount points clean and bright before assembly. Touch up with paint any bare parts showing when assembled.
Finally, check the voltage drop from the B+ terminal at the diode board to the + terminal of the battery. It should be less than .5 volts drop, preferably much less, like .1 or so. Too high a drop means bad connections or wires in the charge circuitry.
A little extra work here now can save a lot of grief down the road. I did a lot of ground improving and cleaning / sealing up etc on all my electrics when the bike was brand new - and it's paid off with 0 problems in 18 years.
Seek, and ye shall find.
One world, Two wheels.