What is a more eloquent way to say "I hope I'm not asking too much"?

I've been emailing back and forth with another professional who has been very generous in sharing a workflow developed at their institution. This professional has gone to great lengths to answer my questions. Given that he has no obligation to answer my questions, I'm starting to feel that I'm overstepping boundaries by asking for more details that would require a higher level of investment for him to answer.

I feel that "I hope I'm not asking too much" is cliche at this point in the discussion. What would be a more sincere way to communicate that the effort is appreciated and helpful, and then follow up with another request while making it clear that he has no obligation to reply. It may also be helpful to note that this would be the last question.

Solution 1:

I think it would be good to come right out and thank the person for his/her generosity in answering all of your questions. It might be easier to thank the person, and ask him/her to tell you if/when your continued questioning is taking too much time, or he/she is too busy to answer than to go the "I hope I'm not asking too much" route... this way the person can politely set a boundary if/when it's necessary. The person helping you will likely enjoy the fact that the help is appreciated.

Solution 2:

Something like If you would be so kind, I have one final question of your expertise... should do. Flattery will get you everywhere.