Filters' configuration splitting

Ok, this should be a little bit easier. I have a smart plug with hlw8012 for power metering.
I always calibrate power readings only the with “calibrate_linear”, but also have other filters for power, which I don’t want to change at all.
So I’m trying to split ONLY the filters configuration. This means keep only the calibrate_linear filter in my main config file and put the rest in another file to be recalled with a <<: !include function. But whatever I’ve tried I haven’t been able to achieve this simple thing. I’m trying with (just the important snippet, the rest is ok):

power:
  ...
  filters:
    - <<: !include common/devices/plugs/gosundSP1/power_filters.yaml
    - calibrate_linear:
      - 0.00000 -> 5.0

It only works if the power_filters.yaml file only has ONE filter, let’s say multiply: 1 (with or without a - ).
I’ve tried to add all the other filters with any YAML syntax imaginable but upon compilation it errors out. Most of the times it cannot recognize that I have 2 filters. Let’s say if I have in my power_filters.yaml:

- multiply: 1
- offset: 2

it errors out with:
" Cannot have two filters in one item. Key ‘multiply’ overrides ‘offset’! Did you forget to indent the block inside the multiply?.
- multiply: 1
offset: 2 "

So it doesn’t recognize the second filter as a separate one. I’ve tried all possible YAML syntax about multiple values ( [ ] or commas or ’ ) but nothing works, even if it’s verified by YAMLLint.
Does anyone have any suggestions, particularly about how to formulate my power_filters.yaml? Or it’s just not doable the way I’m trying?
Essentially I want to split my filters’ configuration and leave just one filter in my main config. (I’ve tried with packages, it also fails, because whatever I’ve tried, the filters in the package are not merged with those in my main config, but overwritten by the latter. So if I have multiple filters in the package file but only one in my main config, the final compilation only has 1 filter in the end).

Does anyone have any ideas?