How to ensure the sketch for a solid boss, consists of both a circle and an ellipse, created using the loft boss feature, turns out perfectly?

May I suggest a different method: Instead of doing a Loft, make the hole based on the circle. The hole will have a horizontal bottom. Then add the incline on the bottom by extruding a triangular profile

To ensure that the sketch for a solid boss, which consists of both a circle and an ellipse created using the loft boss feature, turns out perfectly, you can follow these steps in SolidWorks:

Create Sketches for Circle and Ellipse:

Start by creating a sketch for the circle and another sketch for the ellipse on different planes or locations.
Ensure that both sketches are fully defined and positioned as desired.
Use the Loft Boss/Base Feature:

Go to the "Features" tab and select "Loft Boss/Base" from the dropdown menu.
In the Loft PropertyManager, select the sketches representing the circle and ellipse as your loft profiles.
Adjust Loft Options:

In the Loft PropertyManager, you may have options to adjust the loft settings. Ensure that the options are set according to your requirements. For example, you may want to choose the "Guide Curves" option if you need additional control over the loft shape.
Preview and Confirm:

Once you've selected the profiles and adjusted the loft options, preview the lofted feature to ensure that it looks as expected.
Confirm the loft creation by clicking "OK" in the Loft PropertyManager.
Check for Errors:

After creating the lofted feature, check for any errors or warnings in the FeatureManager design tree or in the graphics area. Resolve any issues that may arise.
Adjust Sketches as Needed:

If the lofted feature doesn't turn out as expected, go back to the original sketches of the circle and ellipse and make adjustments as needed. Ensure that the sketches are fully defined and positioned correctly.