Thank you @kkanade

Unfortunately, I am not ready to mark my post as resolved since your comment does not answer my questions and it will not help others in any way.

1) I asked if "geometrical" way of placing bubble in the flow is valid at all. You haven't directly answered this question. Your answer is difficult to understand. Also, proper capitalization in your writing would be highly appreciated - all lower cases make it more difficult to read. But at least it can be inferred from your answer that "geometrical" way of placing bubble in the flow is in fact valid. Well, while it is good to know that - it would've been even better if you could elaborate a little bit more on the matter.

2) I am aware that I can create a droplet in the flow. I asked HOW to place a bubble in the flow using design modeler. I explained in my post that I tried to do that and I failed.