Magento 2 Layered Price Filter Conditional Query

I’ve been tasked with fixing the price filter on a Magento 2 site.
It works fine with normal products, but a new “grouped_product_price” has been added to Grouped Products as part of a custom module.

I want to apply a condition to the current query which basically says:

If there’s a grouped_product_price attribute value then check that value, otherwise use the normal price

For dev purposes I’m working in vendor/magento/module-catalog-search/Model/Layer/Filter/
Price.php

Once it’s working I’ll be moving this to a module.

This query returns some values:

 $this->getLayer()->getProductCollection()->addFieldToFilter(
            'price',
            ['from' => $from, 'to' =>  empty($to) || $from == $to ? $to : $to - self::PRICE_DELTA]
        )->addAttributeToFilter('grouped_product_price',['gt'=> empty($to) || $from == $to ? $to : $to - self::PRICE_DELTA]);

But it’s an AND query, which isn’t what I want.

I know I’m close to sorting this.

Any ideas?