Settings for lazy-loading and eager-loading can be configured in HTL BID for each slot:
Configuration
Navigate to “Ad Configuration” > “Slot Setup” and expand a Slot
Scroll to the end and click on any attributes or the arrow on the far right to expand the Slot Attributes section, locate the “Eager” checkbox
If unchecked, it will display the “Lazy” checkbox
One input field is required for lazy loading:
Lazy pixels - The pixel value entered determines how far away from the viewport the ad will be requested. The higher the value, the further away from the viewport the ad will be requested. If left empty, the field will default to 350px.