Dear John,

Thank you for using Power Integrations.
First, I noticed that you are using a stand alone PIExpert Suite. If you have a good internet access, I would suggest that you access the online version as updates are coursed through them nowadays. Here is the link: https://piexpertonline.power.com/piexpert/design/index.
It may not present much of difference but in the online version, there is a choice between PIExpert and PIXls for Tiny 4. PIExpert takes care of optimizationsl.

As for your question, there are two different ALG. One which is published in the vendor specifications which is the ungapped ALG and one which you are referring to is a gapped ALG.
What is given to you is simply the suggested Lpri/ turns^2(gapped).
As you gap your core, the inductance/turns^2 of the core lowers and the B-H curve "flattens" or softens on that saturation portion of your magnetics. It is where you actually store the energy in the flyback.
The ungapped ALG of 3C95's does have a certain ALG with a + and - tolerance of 25% or less and still give you the inductance that you want. When you make your transformer, you gap it until you get the target inductance that you want before taping the core for good. Some people put spacers on the sides. But this is more expensive as two spacers are need on both sides to produce that same gap in the center. By scraping off the center of the core, you are gapping it just like putting to spacers on the side. The main difference is just the cost and the reusability(can easily adjust the spacers for other inductance targets) of the core for other projects.

Regards,
Thorin

Hi Thorin,
First of all thank you for your answer. Your answer is very clear and has been very useful.
While I was waiting for someone to help me, I talked to a transformer designer specializing in switching power supply, which broadly told me the same things.
I will follow your advice to simulate online projects.
I wish you a good weekend.
John