Wait a moment. So you sold the same number of books both times, but the checks were for two different amounts. And that's because they didn't pay 100% of what they owed you that first time?
That's...not good.
Soul Mate author chiming in...
Soul Mate pays quarterly, but the royalties earned must be at least $20 EXCEPT in December when they pay you the rest of you you're owed.
They do some--though not a lot--of marketing on their end. In my research, I found they do more than many of the indie publishers out there. Do I wish they'd do more? Of course.
As I've posted before--Soul Mate is a good fit for some, but not all. I plan on submitting a second book to them becuase it's a sequel to my first book, but as for future novels.... maybe. We'll see.
I've had a couple of bumps with Soul Mate but everything was handled professionally, and partially my fault.
Download and read some free samples in your genre from SMP. Look at the covers. If you're still apprehensive then SMP probably isn't a good fit for you. I've read quite a few SMP books and have loved most of them. There was only one or two that I only liked, and none that I didn't like. I feel good about that.
Like Kellie, feel free to PM me if you have specific questions or concerns.