mr rusty
Member
You are worrying too much. Use the filter settings Ilford give. They will most likely be just fine. Nothing to stop you using under-lens filters with a colour head anyway instead of the built-in filters - just zero the filters or move them out of the path if there is a switch/lever to do this. Or, your enlarger most likely also has a filter drawer where you can use above-lens filters.
Even if exposure time does get altered between grades using the colour head filters, once you have set the grade you want to use, you can always run a test strip to fine-tune exact exposure.
After a bit of experience, you will soon get used to your own rig. If you consistently find that using a particular grade on a particular setting always causes under/over exposure, either increase/decrease the magenta & yellow equally to tweak the grade setting appropriately (increasing both filters will increase exposure time) or make a manual exposure time adjustment to compensate. Sounds complicated, but once you have got the "feel", it will come much easier as you will already have expectations of what the results should be based on experience.
Even if exposure time does get altered between grades using the colour head filters, once you have set the grade you want to use, you can always run a test strip to fine-tune exact exposure.
After a bit of experience, you will soon get used to your own rig. If you consistently find that using a particular grade on a particular setting always causes under/over exposure, either increase/decrease the magenta & yellow equally to tweak the grade setting appropriately (increasing both filters will increase exposure time) or make a manual exposure time adjustment to compensate. Sounds complicated, but once you have got the "feel", it will come much easier as you will already have expectations of what the results should be based on experience.


