Layer blend modes and blend if godsend

<p style="margin: 0cm 0cm 10pt;" class="MsoNormal"]<span style="font-size: small; font-family: Calibri;"]Not sure where this post should go, but happy to receive any input on composition. Apologies if in wrong place.
<p style="margin: 0cm 0cm 10pt;" class="MsoNormal"]<span style="font-size: small; font-family: Calibri;"]Below are the works in progress and techniques I used to correct exposure issues, especially regarding the sky on my old 40D with a 10-22 lens. Skies in Greece can be extraordinarily blue, especially in autumn (a sort of second spring). I’m sure real filters could correct the wrong exposure, but they’re notoriously ineffective with wide-angle lens and besides, why put filters in front of your expensive glass when PS can fix the issue? (Please don’t all explain why I’m wrong…)
<p style="margin: 0cm 0cm 10pt;" class="MsoNormal"]<span style="font-size: small; font-family: Calibri;"]In order, the raw capture converted to jpg for this post, the basic multiply mode correction and then the blend if multiply mode.
<p style="margin: 0cm 0cm 10pt;" class="MsoNormal"]<span style="font-size: small; font-family: Calibri;"]My technique involves copying the background layer and changing the blend mode to “multiply”. At first, I was quite happy to go over the edges (which generated artefacts, especially in bright areas) with an eraser.<span style="mso-spacerun: yes;"] I then learnt that right-clicking on the layer properties could allow me to adjust the “blend if” properties (the greyscale slider) to adjust much more finely (and thus save time).
<p style="margin: 0cm 0cm 10pt;" class="MsoNormal"]<span style="font-size: small; font-family: Calibri;"]Renewed apologies if you’re all PS genius and I’m teaching you to suck eggs. If you’re not, I’d be happy to show a walk through.
<p style="margin: 0cm 0cm 10pt;" class="MsoNormal"]<span style="font-size: small; font-family: Calibri;"]Raw:
<p style="margin: 0cm 0cm 10pt;" class="MsoNormal"][img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.23.67/raw.jpg[/img]

Ordinary multiply mode (note artefacts in bright areas).

[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.23.67/without_2D00_blend_2D00_if.jpg[/img]

Whoops, exceeded my file size quota. I'll add it later after I've done some housekeeping.