The ratio of customers to open source users is largely useless. To "convert" users, you need to offer something above and beyond what is available in the open source offering. Unless you have something compelling, people won't "convert" out of altruistic desires. Unfortunately that's not how business works. We found many companies deciding to fork our open source libraries before even considering contacting us (for example, the John Deere homepage https://www.deere.com/en/ uses a forked version of our open source offering)
To "increase the conversion rate" you have to either improve the value of the commercial offering or cripple / remove the open source offering. They seem to be doing the latter.
You think you have plenty of money to spend and it's easy to get licenses for software. Nope. It's often harder than being in a small business. Licenses often mean lengthy RFPs with extensive Legal and Procurement involvement.
Need to try and sneak things under the radar if you want to get them to buy your products.
So in some ways it makes sense to make your enterprise price incredibly high - because the people within large companies will either be able to spend loads of money, or non at all. Very few will be anywhere in between (and will find it very difficult to pay or continue to pay over time).
I'm not even sure if that would have much influence: the line between paying and non-paying might be just the divide between companies where it's hard to get paid licencing approved and companies where it's hard to get unpaid licensing approved. The key to a high commercial open source conversion rate might be targeting industries where lingering distrust of open source is still common.
Certainly you can easily jump to "100%" conversion rate by dropping an open source offering so there's no conversion to rate, but never forget that conversion rate is a bad metric to optimize in this case. You can have a very high conversion rate of a very low number of users very easily, and that doesn't mean you get paid more at the end of the day, though.
Removing/crippling an open source offering can backfire in simple and obvious ways such as killing community goodwill, or crippling any conversion rate momentum you have in existing marketing efforts and conversion paths. It can be a quick way to shrink your entire audience for the project.
So yes, the ratio of customers to open source users is largely useless, but I'd say more for the same reason that any ratio metric fails to account for magnitudes of scale, rather than necessarily blaming individual users on either side of the "conversion fence".