diff --git a/dev-docs/bidders/unicorn.md b/dev-docs/bidders/unicorn.md
index 91360b76cc..f3028816bb 100644
--- a/dev-docs/bidders/unicorn.md
+++ b/dev-docs/bidders/unicorn.md
@@ -10,15 +10,37 @@ biddercode: unicorn
 sidebarType: 1
 ---
 
-### bid params
+## bid params
 
 {: .table .table-bordered .table-striped }
-| Name          | Scope    | Description                               | Example    | Type      |
-|---------------|----------|-------------------------------------------|------------|-----------|
-| `placementId` | optional | Your placement ID | `'rectangle-ad-1'` | `string` |
-| `accountId` | required | Account ID for charge request (provided by UNICORN) | `12345` | `integer` |
-| `publisherId` | optional | Account specific publisher id. | `'67890'` | `string`  |
-| `mediaId` | optional | Publisher specific media id. | `'example'` | `string` |
-| `bcat` | optional for Prebid.js  | Blocked IAB categories | `['IAB-1', 'IAB-2']` | `[string]` |
+| Name          | Scope                  | Description                                         | Example              | Type       |
+| ------------- | ---------------------- | --------------------------------------------------- | -------------------- | ---------- |
+| `placementId` | optional               | Your placement ID                                   | `'rectangle-ad-1'`   | `string`   |
+| `accountId`   | required               | Account ID for charge request (provided by UNICORN) | `12345`              | `integer`  |
+| `publisherId` | optional               | Account specific publisher id.                      | `'67890'`            | `string`   |
+| `mediaId`     | optional               | Publisher specific media id.                        | `'example'`          | `string`   |
+| `bcat`        | optional for Prebid.js | Blocked IAB categories                              | `['IAB-1', 'IAB-2']` | `[string]` |
 
 `publisherId` as `integer` is also supported on Prebid.js
+
+## Ad slot position signals
+
+For each bid request the adapter measures the ad slot's on-screen position,
+geometry and viewability, and sends it in the OpenRTB request it builds. This is
+scoped to the UNICORN request only — nothing is written to shared First Party
+Data, so no other bidder is affected. No configuration is required.
+
+- `imp.banner.pos` — OpenRTB AdPosition (`1` = above the fold, `3` = below the
+  fold). A publisher-declared `ortb2Imp.banner.pos`, if present, is used instead
+  of the measured value.
+- `imp.ext.adslot` — `{ ver, ratio, fixed, sticky, w, h, x, y }`: `ratio` is the
+  visible-area ratio (0–1), `fixed`/`sticky` flag a fixed/sticky ancestor, and
+  `x`/`y`/`w`/`h` are the slot's document-relative position and rendered size in
+  CSS pixels.
+- `imp.ext.gpid` — the Global Placement ID, forwarded from `ortb2Imp.ext.gpid`
+  (set by the `gpid` / `gptPreAuction` module) when present.
+
+The slot element is resolved in this order: `ortb2Imp.ext.data.divId` → the GPT
+slot mapping (`getSlotElementId()`) → the ad unit code. Set
+`ortb2Imp.ext.data.divId` when the ad unit code is not the div id and GPT is not
+defined at auction time.