I think you are using a regulator which is more commonly called "AC Fan Dimmer" These low cost dimmers are made up of a Potentio Meter, Triac, a diac and some passive components mounted on a small pcb. All of these dimmers made up of Triacs control the output voltage by controlling phase or better said chopping the 220VAC cycle. Since they only control firing angle without looking at the RMS value of the output voltage their output strictly depends upon input voltage. Also when the various AC fans have difference in their electrical parameters therefore with some fans these dimmers seem to be working fine. In fact these low cost dimmers don't actually regulate but vary the output voltage by controlling the firing angle of the Triacs.
What you can do is (In my opinion) open up your dimmer circuit and compare it with any dimmer circuit such as this one:
**broken link removed**
Identify the R1(10K) in your circuit and increase its value so that the firing angle of triac can become a little more late.
the other thing that you may do is check what capacitor value does your 220V AC ceiling fan uses. normally they use ~2.2uF to ~3.5uF value you may reduce this capacitor value to reduce your fan speed.
Both the options will affect the maximum speed of the fan, therefore you will need to find component values that are reasonably good for you at both max and min speed.
Hope it helps
Regards,
Asim