There is no set rules when it comes to Cap1 and CLI's. Yes its probably a bucket card. I do know people (outside of here) who keep a high balance and they get auto's left and right. So they can run up the balance even more. More interest laced payments. Cap1 makes more $. They wont listen to me to pay it down. So even it you did get one. Probably a few hundred or just maybe more.
I agree with the others it's probably bucketed, but they do like heavy usage. I just went from $2000 to $3500 after 7 months with a lower tier card by pumping a lot of usage through it (avg of $2k/mo during that time). I let the balance get high at times (over $1500 at one point) before paying off but closing balances were never higher than 19% and 3 of them were 5% or less.
Yes it's probably bucketed, sadly. That said, if you're so inclined, I believe I have heard 60% being thrown around as a percentage to try to use and pay off in full (no need to carry and pay interest). Also note that you would have to do this for a few months, not just one month.
Indeed, it might be the reason that my Cap1/Walmart is bucketed to a $500 CL for several years, because it is in SD...
Fico8: EX~EQ~TU~840 (12 month goal~850).
Yes, Capital One normally likes to see moderate-to-heavy usage to approve a CLI, @JcT21. Your $1200 spend on a $3600 limit isn't what I would call heavy usage and maybe on the low end of moderate at about 33%. I've grown a Capital One card from Platinum ($1K limit) to Quicksilver ($28K limit) over many years. I posted many data points at >This Thread< (see thread message 34) and you can also reference Capital One approval data points at >This Thread< by @Curious_George2.
Based on those data points, it appears to me that about 45% of credit limit is roughly around the "magic number" to hit or eclipse. So I would expect a decline. However, do that for another month and you may get an approval. 
With a relatively decent CL of $3600 on the card, I question whether it's truly bucketed. Low limits with Capital One don't always mean bucketed cards, as my example proves.
Lately, I've gotten some with unexpected $1K CLIs Capital One from $25K to $28K without putting even moderate spend on the card, but this seems atypical.
Anecdotally from reports here/reddit/experiences of a few personal friends, I'm also under the impression that in addition to heavy usage, Cap 1 generally is more reluctant to give big CLs if you already have multiple highish to high limit CLs (ie they don't want to be your're 4th or 5th $15K+ card etc.)
Only "heavy" usage my Cap1 card will ever get any more is dependant on how many pairs of socks gets thrown on top of it in that drawer 
