Transit through London with EU residence permit (Tunisian passport) - risky or fine?

Hi everyone, I’m a Tunisian citizen living in Germany with a valid residence permit and I’m planning a trip to Malta. My route is Berlin to London and then London to Malta on the same day, but the flights are booked separately. I won’t have any checked luggage and I plan to stay entirely airside during the transfer without entering the UK. I do have a confirmed onward ticket to Malta and a return ticket back to Germany a few days later. From what I’ve read, it might be possible to transit airside without a UK visa if you hold an EU residence permit, but I’m concerned that with separate tickets I might be required to go through border control or be denied boarding. Has anyone been in a similar situation, and is this realistically doable or too risky?