One of the things I have learned here at BSG is the contagious attitude that these c**ts are doing you a favour by asking to see more material.
There is a pervasive sense of cowardice here evidenced by the thread starter's post: He wonders if he should email to ask for feedback. The implication being that he does not want to upset the producer or appear to be a pest.
These companies need your excellent work more than you need them.
They are the store; they make money by selling produce; they do not create produce, they solicit it and make a show out of what's received and then sell that show (produce). They are not writers; they cannot write. They need written material. Most of what they receive is shite.
Most of what they produce is shite via mediocrity.
If what you are writing (and have written) impresses you, then you can relax and stop behaving & thinking from the perspective that prod companies are gods and you are but a mere piece of grovelling dirt asking them to examine a piece of filthy toilet paper.
Submit with confidence and mark the date and if they don't get back to you within 5 weeks, send it off to another company. If they ask for more material, send it with a note informing them that you want a reply within a month or else you will submit the material elsewhere.
You gotta be polite and yet hard nosed. This is serious business. You don't act like a f**ken wimp when you go to the newsagents or the grocery store or the garage or your job, so why act like it when you are selling your writing?
They need writing. You have it. You send it. If it fits what they are looking for, they'll buy it. If it doesn't fit, they'll reject it. That rejection is not an objective assessment of the quality of your work. It is merely saying, "We are looking for triangles and you sent us a circle".
You have what you believe you can have.